We intend to characterize the DNA-covalent binding of electrophilic carcinogens as to the structure of the adduct and the nucleotide specificity of the carcinogen. DNA fragments containing characterized DNA lesions will be cloned into E. coli strains containing normal and defective repair systems. We will investigate the molecular events required for repair (or misrepair) of these lesions, including endonuclease action, induction of error-prone repair, and nucleotide sequence changes. From the data obtained we will construct an acceptable model for the mechanism of carcinogen-induced frame-shift mutagenesis.